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Biochim Biophys Acta. 2008 Jul-Aug;1777(7-8):711-8. doi: 10.1016/j.bbabio.2008.03.023. Epub 2008 Apr 3.

Three-dimensional structure of respiratory complex I from Escherichia coli in ice in the presence of nucleotides.

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  • 1Medical Research Council, Dunn Human Nutrition Unit, Wellcome Trust/MRC Building, Hills Road, Cambridge CB2 2XY, UK.


Complex I (NADH:ubiquinone oxidoreductase) is the largest protein complex of bacterial and mitochondrial respiratory chains. The first three-dimensional structure of bacterial complex I in vitrified ice was determined by electron cryo-microscopy and single particle analysis. The structure of the Escherichia coli enzyme incubated with either NAD(+) (as a reference) or NADH was calculated to 35 and 39 A resolution, respectively. The X-ray structure of the peripheral arm of Thermus thermophilus complex I was docked into the reference EM structure. The model obtained indicates that Fe-S cluster N2 is close to the membrane domain interface, allowing for effective electron transfer to membrane-embedded quinone. At the current resolution, the structures in the presence of NAD(+) or NADH are similar. Additionally, side-view class averages were calculated for the negatively stained bovine enzyme. The structures of bovine complex I in the presence of either NAD(+) or NADH also appeared to be similar. These observations indicate that conformational changes upon reduction with NADH, suggested to occur by a range of studies, are smaller than had been thought previously. The model of the entire bacterial complex I could be built from the crystal structures of subcomplexes using the EM envelope described here.

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